EXPLANATION OF TERMS. 401 



form shells, however, are not always incurved, the top 

 bending downwards or being erect. 



Reflected, Turned or folded backwards, as is the thick- 

 ened outer lip of the common garden, and many other 

 of the terrestrial, snails. 



Reverse Shells, are such as have the aperture opening 

 on the left side when it is placed in front of the spec- 

 tator. 



Sinuatedi or waved. Any part whose margin has one 

 or more undulations ; this appearance is produced by 

 a projecting lobe being followed by a notch or hollow 

 more or less deep. The outer lip of Struthiolaria and 

 several of the StromU are sinuated, but the latter so 

 much so as to form abrupt lobes and corresponding 

 notches. 



Sessile. Destitute of any support or peduncle, as in the 

 shell of the Anomia. Those of Terebratula, on the 

 contrary, are elevated in some degree, on a peduncle, 

 and are termed pedunculated. 



Siphon. A sucker: a fleshy process, generally long, 

 cylindrical, and hollow ; protruded by the carnivorous 

 and testaceous animals from the base or channel of 

 their shells. The same term is given to the slender 

 shelly tube which connects the chambers of cephalo- 

 pod shells, or the Nautili. 



Spire. Those volutions of a spiral shell Avhich are 

 above the lowest or body-whorl, collectively form the 

 spire of the shell, whatever shape it may assume. 

 The variations in the form of this part are numerous. 

 In some it is excessively lengthened j in others it is not 

 even raised above the body- whorl. In Planorbis the 

 spire is sunk, while in Cyprcea it is so small as 

 only to be seen when the shell is young, after which 

 it is covered over by the enlargement of the body- 

 whorl or principal volution. 



Squamose. Having the appearance of scales. 



